Efecto de los mecanismos de defensa de las plantas en la eficacia de transmisión por semilla de los virus

Resumen

The two main plant defense mechanisms against parasites are resistance and tolerance. Despite accumulating evidence indicates that tolerance is as widespread and successful as resistance, it has been comparatively much less studied. As a defense mechanism, tolerance is expected to affect parasite fitness, and particularly its capacity for dispersal. However, the consequences of tolerance for the rate of parasite transmission are largely unknown, especially for the efficiency of seed transmission rate. Seed transmission rate is a main mode for plant parasite spread. Therefore, the study of how plant tolerance influences this trait will contribute to develop more efficient control strategies, which would have significant economic, social, and ecological benefits. Using Arabidopsis thaliana and two isolates of Turnip mosaic virus (TuMV; JPN 1 & UK 1) as host-parasite system, this study analyzed how do viruses evolve their seed transmission rate in the presence/absence of host tolerance. To do so, seeds from four different plant genotypes, each one infected with lineages evolved from JPN1 and UK1 ancestors in host populations with different levels of tolerance, were grown and tested for the presence/absence of the virus. The efficiency of seed transmission was also compared with the effect of virus infection in various plant traits to gather information on the possible processes underlying the evolution of seed transmission rate. The results showed that lineages evolved in highly tolerant host populations had significantly higher seed transmission rate than the lineages evolved in less tolerant hosts or than the ancestral viruses. The increase of seed transmission rate was then found to be associated with the rise of the host tolerance, and also with higher viral accumulation within the host. Additionally, this work presents tentative evidence that for the increase in seed transmission rate to occur, this parameter must be decoupled from other infection traits related with the growth and reproduction of the host. Overall, this work provides novel insights on the processes of parasite adaptation to host tolerance and shows that improved plant defenses not necessarily result in a negative effect on virus fitness.